In the field of automated measuring and testing equipment, one problem that must be addressed is the provision of test samples to, and removal of tested samples from, such equipment. A sample is inserted in the tester, which then automatically performs various tests, and the sample is then removed after testing and replaced with another sample. Sample changing can be done by hand. However, manual changing is slow, can result in contamination of the samples and requires the presence of an operator which partially defeats the purpose of automating the test equipment.
Accordingly, in the field of materials testing, it has been a general practice to employ automated devices for acquisition of a sample to be tested, transport of that sample to a testing apparatus, retrieval of the tested sample from the testing apparatus, and finally return of the sample whence it came or else provision of the tested sample to appropriate disposal. Often, such devices, particularly owing to their automatic nature, are designed or adapted to engage, transport and release samples of a predetermined size.
One example of a such a prior art automated testing device which handles predetermined size samples is a nuclear magnetic resonance (NMR) spectrometer, which includes a magnet chamber and a cylinder. Samples of material to be tested by the NMR spectrometer must be conveyed into the interior of the magnet chamber and, to that end, a sample is dropped into the cylinder and falls therethrough into the magnet chamber. After testing, the sample is ejected from the magnet chamber by any of various mechanisms.
An illustrative example of a magnet chamber 113 and a sample changer 117 for such an NMR spectrometer is shown in FIG. 8. Such a device is typical of NMR spectrometers available from Bruker Instruments, Inc., Billerica, Mass. Magnet chamber 113 is provided with a cylinder 115. Material samples are tested in magnet chamber 113 and such samples are inserted in and removed from chamber 113 via cylinder 115.
Magnet chamber 113 can be used for testing samples of both solid and liquid materials. Liquid samples are contained in sample holders made of glass which are easily broken. Consequently, it is necessary to handle the sample containers firmly but gently. Liquid sample holders are illustratively handled by material handling apparatus 117 which includes a vertical cylinder 119 and piston 121 mounted on a rotatable arm 123. The lower end of piston 121 is provided with a pneumatically-controlled pincher 137 for picking up and carrying a liquid sample holder. Arm 123 is rotatably supported on motorized pole 125 by upper and lower fixture rings 127 and 129 each connected to arm 123, and by resting ring 131 on which lower fixture ring 129 rests. Pole 125 is also provided with a pipe or tube 133 which supports magazine belt 135. Magazine belt 135 is configured to hold a plurality of liquid samples, and is rotated with rotation of pipe 133 so that different samples can be presented at different times to pincher 137. Cabinet 139 provides controls for movement of pipe 133 and pole 125. Pincher 137 with cylinder 119 and piston 121 can be moved horizontally or radially along arm 123, and may be moved azimuthally by swinging of arm 123 by rotation of pole 125 caused by cabinet 139. Pincher 137 is connected to the lower end of piston 121, and can be controlled to open and close about a liquid sample at belt 135 and cylinder 115. Cylinder 119, piston 121, arm 123 and pole 125 can thereby move pincher 137 between belt 135 and cylinder 115. Once the sample holders are inserted into cylinder 115, they are conveyed pneumatically to the interior of magnet chamber 113 and subsequently pneumatically ejected from chamber 113 after testing is completed.
The material handling apparatus 117 functions well to handle the delicate liquid sample holders. Magnet chamber 113 can also be modified to handle solid sample holders to enable the spectrometer to automatically test such samples. Typical solid sample holders are considerably smaller than liquid sample holders and are much more rugged. In particular, as shown in FIGS. 9 and 10, solid samples are typically disposed in a holder 151 which includes cap 147 and hollow ceramic tube 149. In one version of holder 151, cap 147 is tightly press-fitted on tube 149 whose opposite end is closed. Once inside magnet chamber 113 of the spectrometer, in accordance with well-known NMR spectroscopy techniques, holder 151 is rapidly rotated by compressed air, and for this reason is called a "rotor".
Apparatus 117 is obviously complicated and expensive and well-suited to handling fragile holders such as the liquid sample holders. Since the ceramic solid sample rotors are much more rugged than the glass liquid sample holders, it is no longer necessary to use the aforementioned complicated pincher mechanism to delicately transport the rotors between a moving supply belt or other source of supply and the spectrometer, if that were possible.
Furthermore, difficulty has been encountered with regard to the above-mentioned modification of magnet chamber 113 to handle rotors. Inside magnet chamber 113, the toothed or ratcheted edges of cap 147 are engaged by compressed air to rotate the sample in a technique known in the art as "magic angle" spinning. This rapid rotation, for proper testing, must occur at a particular angle with respect to the magnet chamber 113. This "magic angle" is 54.7.degree. with respect to the direction of the magnetic field of magnet chamber 113. In order to place a rotor 151 in the proper position at the proper angle within magnet chamber 113 for testing, it has been found necessary to require the rotor, when dropped into magnet chamber 113, to follow a winding path to the location within the magnet chamber where it will be tested. One example of such a path is shown in International Patent Application WO 89/11646 published Nov. 30, 1989 for "NMR-Spectrometer With Sample Exchanger" in the single figure thereof, which published application is hereby incorporated by reference herein. Typically, a blast of compressed air is used to insert the rotor into, and a separate blast of compressed air is used to eject the rotor from, that location. Particularly because of the winding path which the rotor must follow to and from the location within magnet chamber where it is to be tested, difficulty has been encountered in properly seating the rotor 147 at that location so that it can be tested.
Accordingly, there is a need for a sample changer providing rapid, easy changing of samples of solid material to and from a device that tests such samples. The present invention fulfills that need.